1. Field of the Invention
The field of the present invention is that of the fabrication of parts in composite materials, and in particular that of the production of parts by an in vacuo resin transfer molding (RTM) process.
2. Description of the Related Art
The RTM process is routinely used in the fabrication of aerospace parts. It consists in the fabrication of a fiber, preferably woven fiber, preform that is placed in a closed mould in which it receives, by injection at a low pressure, a thermosetting resin of relatively low viscosity. The main steps of the process are placing the fibrous preform in the mould, filling the mould by injection and polymerizing the resin. A vacuum is generally established in the mould to enable the resin to flow better and therefore to eliminate defects such as bubbles and voids.
This technique is used notably for the fabrication of compressor blades, and in particular fan blades, for aeronautical turbomachines. To this end, as indicated in the applicant's patent application EP1526285 a fiber structure is woven to produce a preform that will serve as a structural reinforcement for the part. Present performs are three-dimensional and increasingly complex. In particular, in the case of a fan blade, the preform has a great length compared to its other dimensions. The preform obtained is thus relatively flexible and is deformed by the action of its own weight.
Moreover, to fabricate a fan blade, a multitude of warp and weft threads are used which must thereafter be terminated once weaving is finished. When fabrication of the fan blade preform is finished, it is necessary to cut it to size and to cut all these threads, which are generally carbon threads, allowing an excess length to project from the preform. One example of a device suitable for this cutting operation is given in patent application WO 2007/111574. However, in the first place, this operation, effected with a cutting tool, is difficult to carry out because of the resistance to cutting of the carbon strands and because of the deformation of the performs. Secondly it is effected on a cutting frame from which the preform must thereafter be extracted to transfer it to the injection mould. With a preform that deforms, this manipulation is relatively difficult and causes uncertainties as to its position within the injection mould.